The present invention relates to a color adjusting method to be implemented in a computer equipped with a full-color display and, more particularly, to a color changing method which is suited for sales presentations of commodities, appearance simulations of buildings or color designs for industrial products by using a function for simulating the changes in the object colors of natural images due to ambient changes such as the weather of the actual world or the time or changes in the object colors in an identical ambience.
When a color image is to be displayed in a full-color CRT by the color adjusting method of the prior art, the display colors are determined to indicate the three primary color components, i.e., red (R), green (G) and blue (B) colors. In the prior art, the values of the RGB are sometimes inputted manually and directly by the operator, but it is difficult for the operator to discriminate the correspondences between the RGB components and the actual color. In the full-color natural image editor (which is known under the trade name of "CANVAS") of ADS Corporation, for example, there are used as the expression of the color not only the RGB components but also the hue (H), saturation (S) and value (V) of the color, and a sample color set is prepared for selections so that the color may be adjusted as if it were mixed on the palette of paints.
The method of the prior art for changing the colors of a color image is exemplified by either a color change (i.e., the characteristic evaluations of a variety of HIS color models according to the lecture of Japanese Photo Survey Association made by Fukue in October, 1986, which will be referred to as "Reference 1") by HSV, HSI or HSL level or a color change (i.e., O plus E No. 110, Full Color Image Processor SHAIP and Its Application made in January, 1989, which will be referred to as "Reference 2") for setting the color conversion by using a look-up table.
The method of changing the colors of the picture element values of a color image in the three-dimensional three-primary color space having plotted the picture element values is exemplified by the method (which will be referred to as "Reference 3") of changing the colors of the individual picture elements by presuming a plurality of color vector in the three-primary color space to determine the separated components of the color vector of the plotted individual picture element values and by changing the color vector thereby to use both separated components and the changed color vector like the present invention in Japanese Patent Laid-Open No. 63-237172.
According to this method, as shown in FIG. 25, in the three-dimensional color space, the three primary color components of the individual picture elements in a target color region of a color image are assumed be located in a plane which is composed of a black (i.e., origin), an object color vector Cb and a source color vector Cs. With this assumption, the individual picture elements are separated into the components of the above-specified two vectors and are used as the intermediate coordinates of the two-dimensional individual picture elements, and the color region is then changed into a desired color by calculating the changed three primary color components from the intermediate coordinate values, the light source color vector Cs and a second object color vector Cb' newly obtained. So long as the aforementioned assumption holds, this method is enabled by separating the light source color and the object color to change the object color of an image having a reflection although this has been difficult according to the preceding color changing methods. Since the reflected light appears as a component for the light source color vector of each picture element value in the three-primary color space whereas the remaining lights appear as the components for the object color vector, the color of the image having the reflection can be changed by changing the object color vector.
Although not the process for changing the color of an object, there is another color image processing method (as disclosed in International Journal of Computer Vision No. 1, Vol. 2 (1988.6) by G. J. Klinker, which will be referred to as "Reference 4") using the separated components of the color vector of each picture element value plotted by presuming a plurality of color vectors. In this Reference 4, G. J. Klinker et al. have accomplished the following examinations: 1 Under such a special photographic circumstances in which only one point source exerts influences as a light source for an object, a colored glossy object (made of plastics) is photographed by a CCD camera. Then, the experiments are accomplished by analyzing the three-primary color space plotted with the picture element values of the color image obtained. 2 In accordance with the distribution of the picture element values, the object color vector and the light source color vector are extracted from the dense state of the picture element values. This method has determined that the individual picture element values of a common object region are distributed inside of and in the vicinity of the parallelogram defined by the aforementioned two vectors. 3 G. J. Klinker et al. have proposed that, in case the individual picture elements value in the common object region are approximated as the points in the parallelogram of the two vectors, their positions in the parallelogram are characteristic values depending upon only the positions of the picture elements in the object region. 4 Thus, they have succeeded in eliminating the high-light components from the color image by separating the individual picture element values of the common object region into the aforementioned two vector components to eliminate the specular reflection components (i.e., the source color vector components).
However, the prior art thus far described has the following problems:
(1) In the color adjusting case: There is considerable gap between the numerical values of the color data and the adjusted actual color no matter which of the RGB or HSV might be used for expressions. Certain devices have been known in the prior art for facilitating the correspondence with the perceived color not by inputting the numerical values of the RGB or HSV but by inputting the coordinates in the region in which certain characteristic amounts smoothly change in dependence upon the positions. However, the color mixing belongs to the additive color mixing (in which the three primary colors are mixed into white) and is different from the familiar color mixing of pigments, i.e., the substractive color mixing (in which the three primary colors are mixed into black). This mixing makes it remarkably difficult to adjust a desired color merely by instructing and synthesizing the components.
Certain methods of the prior art present sample colors. Since all of these sample colors are to be displayed one time, the intrinsic three-dimensional structure of the RGB is confined in the two dimensions so that the order of the sample colors is not natural. Moreover, the number of the sample colors is short for reminding the number (0 to 255 for each of the RGB, i.e., 16,770,000) to be displayed on the CRT.
In case, on the other hand, the aforementioned color adjusting method is used for the color changing simulations, the color obtained as a result of the adjustment is used merely on the spot but may have to be stored for another use if an excellent color is adjusted. In this case, moreover, conveniences are not obtained unless a brief description is attached to the color.
The color changing simulations have a problem that calculations are extensive and take a long time.
(2) In the color changing case: In the prior art, the method of the Reference 3 is superior to the other methods of the prior art in the naturality of the color changes but has the following problems:
The first problem is that the method is insufficient for applications to a general color image. The method of the Reference 3 has assumed that the three primary color components of the individual picture elements in a target color region are located on the plane, which is defined by the black color, the object color vector and the light source color vector, in the three-primary color space. This assumption has been made on the image which is taken under remarkably special circumstances. This assumption can be applied to the image, which has been objected by using a circuit for changing the color of an image inputted by a scanner or a color camera in accordance with the shadow obtained by a TV (monochromatic) camera, but not to a general image. In the general color image, the color of an object region in an image is not exhibited only by the influences of the color and amount of a main light source, but the color obtained by the influences of the light (e.g., blue light) of a substance (e.g., sky) existing around the object is also added to the color of the object. When the image is to be photographed or inputted by an image input device, its characteristic color is added to the real color. In the three-primary color space having plotted the picture element values, the linear summation of the color due to the influence of a light, which is emitted from a substance existing around the aforementioned object, and the color obtained by the photographic input device appears as a vector joining the start point of the object color vector and the origin (i.e., black). In the general color image, therefore, it is difficult for each picture element to be approximated by a color in a plane which is defined by the three colors, i.e., black, the object color vector and the light source color vector.
The second problem is that a color change in high fidelity to an original image cannot be accomplished. Assuming that each picture element value be a point in a two-dimensional plane defined by the object color vector and the light source color vector, according to the method of the Reference 3, the color change is accomplished by calculating the components of said vectors for each picture element and by using the calculated component and the vector after the change of the object color vector. However, the real picture element value is distributed not only in said two-dimensional plane but in the vicinity of the same. The distance between the picture element value existing in that vicinity and said plane raises causes not only noises but also the local subtle color texture of the object region and is not eliminated but desirably left. Since the information of the texture of that object region are lost by said method, it is impossible to accomplish the color changes in high fidelity to the original image.
The third problem is the susceptibility to the influences of the light source color. According to the Reference 3, the vector appearing as the randomly scattered components in the three-primary color space, in which the individual picture element values are plotted, are used as the object color so that the color change is accomplished for said object color. Since, however, this object color is subjected to the influences of a light source, disadvantageous or unnatural color change of the object region of the color image is caused, when a design is to be made by the color changing function for the color of an industrial product, which matches the landscape in case the product is placed in the natural ambience. In case a light source color is apart to some extent from the white color for the photography of an image taken from a product having an existing product color when a new color for the product is to be designed (in the landscape of a sunset glow, for example, the sky is red so that the light source color is also red), the product takes the color of the light source. If the candidate color, if any, of a product is used as the color of the object region changed, it does not match the background landscape (i.e., the landscape of the sunset glow in the aforementioned example) but becomes unnatural. If the product of said candidate color is actually placed in said ambience, the product fails to look in said candidate color (in the aforementioned case, a white product takes the red color).
The fourth problem is that the light source color and amount cannot be changed.
The fifth problem is that it is impossible to change the color which is established by the influences of the light coming from an object surrounding the target.